Aramid cord has found a position as a tire reinforcing material for tire casings and belts based on its exceptional properties related to tire performance. For example, its high modulus and strength characteristics contribute to reduced tire weight, lower running temperatures, lower rolling resistance, improved tread wear, improved handling and improved fatigue resistance. The challenge aramid cord faces as a reinforcing agent for tire applications is adhesion of the cord-rubber composite (see "Radial Truck Tire Aramid Reinforcement," paper 45, 126th ACS Rubber Division Meeting, Denver, Colo., Oct. 23-26, 1984; "Aramid Fibers and Adhesion to Elastomers: Applications and Performance," Rubber World 215 (2) page 30 (1996); "Fiber Reinforcement in Tires: An Overview," Tire Technology International, (1993) page 28).
The present invention relates to a sulfur-vulcanized rubber compound comprising a sulfur-vulcanizable rubber, sodium thiosulfate pentahydrate and a bismaleimide which provides improved adhesion between aramid cord and the rubber composition of this invention.